1. Field of the Invention
This invention relates to a molded casing protector and, in particular, a drill pipe, string of drill pipe or drill collar having molded thereto casing protectors comprising annular rings of an oil impermeable and gas impermeable synthetic resin. More particularly, the present invention relates to such drill pipe or drill collar and a method of protecting well casing from damage, wherein the drill pipe has molded thereto casing protectors comprising annular rings of an oil impermeable and gas impermeable synthetic resin, the casing protectors having a slick, hard outer surface for substantially non-damaging contact with the casing.
2. Description of the Prior Art
In the operation of rotary drilling rigs, the rotary drill pipe extends downwardly through well casing and the drill pipe is provided with a plurality of sections held together by means of coupling connectors which are of considerably larger diameter than the normal diameter of the drill pipe. When the pipe is in operation, there is the tendency that the drill rod will whip in the casing or in the hole, causing contact between the coupling connectors and the casing, having the effect of damaging or scarring the casing. Moreover, since an extremely long drill pipe is generally necessary, due to the flexibility in the drill pipe due to its length, and due to the fact that most wellbores are far from being perfectly straight, there is a tendency for the drill pipe, particularly the coupling connectors and drill collar, to strike and rub up against the casing both during the drilling operation and during withdrawal and insertion of the drill collar and drill pipe into the hole.
In the past, much of the concern has been associated with protecting the drill pipe from damage. The early attempts have involved protecting the pipe by the use of protectors such as thick rings of rubber or the like mounted on the pipe at spaced locations along its length, the bumpers serving as shock absorbing bumpers for engagement with the well casing when the pipe is forced laterally within the casing. Examples of this type of drill pipe protector can be found, for example, in the following: U.S. Pat. Nos. 1,608,873 to Werner; 1,841,929 to Barclay; 1,863,823 to Barclay; 2,045,629 to Bettis; 2,722,462 to Tschirley; and 3,588,199 to Hopmans.
The above type of drill pipe protectors suffer from various defects. For example, a quite serious defect of this general type of drill pipe protector has been the tendency for the drill pipe protector to lose its grip and slip down along the pipe, due to the lubricating action of the liquid to which the drill pipe protector is exposed in the casing. Also, such drill pipe protectors comprising thick rings of rubber require extremely long mounting times, thereby providing an economic disadvantage. Moreover, this type of drill pipe protector, as well as all others previously developed, fail to adequately cope with the environmental downhole conditions, the downhole conditions being very hot, under high pressure, with a highly abrasive atmosphere. Accordingly, the rubber drill pipe protectors have been frequently stripped off or damaged to a great extent and, even when not stripped off, moisture can work its way in between the protector and pipe, thereby causing moisture to collect and, as a result, setting up conditions for rusting. Moreover, the abrasive environment created by the presence of sand in the hole tends to increase rather than prevent damage to the casing due to the sand which becomes imbedded in the rubber drill pipe protector, causing the formation of a grinding surface in contact with the well casing.
Various attempts have been made to improve the characteristics of the rubber drill pipe protector, so as to provide for a better hold between the drill pipe protector and drill pipe. One such attempt has been to incorporate various materials within the drill pipe protector, thereby creating a product with greater strength. The use of glass fibers for this purpose is illustrated in U.S. Pat. 2,943,009 to Mirsky.
Most attempts to improve the conventional rubber pipe protector have involved some sort of metal sleeve incorporated within the rubber pipe protector, and some sort of hinge, clamp or other suitable member to act together with the metal sleeve to maintain the drill pipe protector in firm contact with the drill pipe. Examples of this type of drill pipe protector can be found, for example, in the following: U.S. Pat. Nos. 1,894,519 to McLaine; 1,940,332 to Smith; 1,965,730 to Williams; 1,965,998 to Williams; 1,974,546 to Shipley; 2,897,016 to Baker, 3,129,982 to Fawick; 3,164,216 to Hall; 3,425,757 to Minor; 3,449,022 to Minor; and 3,528,499 to Collett.
A conventional type of the foregoing drill pipe protector comprises an annular elastomeric, i.e., rubber sleeve-like body having a metallic reinforcing band imbedded therein. The outer layer or portion of the elastomeric body on the outside of the reinforcing band is usually substantially thicker than the inner layer, and therefore possesses relatively more elasticity. The necessary frictional engagement of the inner layer with the drill pipe to prevent the drill pipe protector from slipping is conventionally obtained by tensioning the protector about the drill pipe, by radially compressing the inner layer between the drill pipe and reinforcing band. In most typical drill pipe protectors of this type, the annular body and its imbedded reinforcing band are longitudinally split with the protector being constricted about the drill pipe by a latch mechanism which draws the ends of the protector together at the split.
While this type of drill pipe protector does eliminate some of the problems inherent in the use of annular ring of rubber, certain major problems still exist. In this regard, there is a serious problem in obtaining the desired frictional engagement of the inner layer against the drill pipe to prevent slippage without compressing the inner layer beyond its maximum modulus of elasticity. In this respect, when there is excessive compression of the inner layer, the elastomeric material rapidly deteriorates by losing its elasticity, resiliency and recovery capabilities thereby effectively reducing the ability of the device to act as a protector.
Because of this problem and because of the conventional utilization of rubber for both the inner and outer layers, this type of drill pipe protector is subject to the same types of problems as encountered with a stretched rubber drill pipe protector. Here again, sand grains tend to imbed in the outer rubber surface, and, as a result, the drill pipe protector acts as a grinding wheel and provides absolutely no protection for the well casing. Moreover, high pressure gas tends to impregnate the rubber, and the oil in the mud deteriorates most rubber products. Furthermore, as a result of the loss of elasticity and grip, chemicals, mud, salt water, etc. tend to get under the rubber, causing corrosion of the drill pipe. For this reason, when the drill pipe is removed from the well, it is generally necessary to remove the drill pipe protector so as to reduce as much as possible this problem of corrosion. This, of course, is costly and extremely time consuming.
One further type of protector which has been previously developed to protect drill pipe is exemplified by that type of protector which has an outer wear surface, such as a ceramic or metal outer surface. Examples of this type of protector can be found in the following: U.S. Pat. Nos. 3,480,094 to Morris; 3,667,817 to Kellner; and 3,697,141 to Garrett. This type of protector is absolutely without any function whatsoever in a well which is cased, since the outer wear surface of the protector tends to rub against and severely damage the casing. Considering the relative cost of replacing damaged casing versus the cost of replacing damaged drill pipe, much more consideration should be given to maintaining the casing free from damage.
As evident from the above, most previous devices have focused on protecting the drill pipe from damage, rather than protecting the casing from damaging contact with the drill pipe, specifically, the coupling connectors of the drill pipe. Certainly, it can be concluded that these previous attempts have been ill focused, and, noting this, the present invention has endeavored to eliminate the deficiencies of the prior art by providing a casing protector free from the disadvantages described above which, in addition to protecting the casing from damage in contact with the drill pipe or drill collar, further protects the drill pipe and drill collar from damage and corrosive attack.